Active sound control systems often require, in addition to actuator and electronic control components, specialized sensor devices. The requirements associated with such sensors to a large part are determined by the particular active control approach employed, as well as the kind of performance expected of the sound controlling system. One type of sensor is the accelerometer, which measures the acceleration of a system, body or surface along one or more axis of acceleration.
These sensors are often used as components of instrumentation packages employed on missiles, satellites or other rocket payloads, aircraft or other mechanisms in which acceleration or vibration can be quite severe. When in employed in such environments, weight becomes a critical variable. A 10 gram weight differential at rest becomes a 150 gram weight difference during a 15 G acceleration event.
While various electro magnetic accelerometers offer high levels of sensitivity and good performance in terms of size and efficiency, these electromagnetic devices are often very sensitive to EMI and aren't always physically robust. The hardening of these devices to EMI almost invariably causes an increase in physical size, weight, sensitivity and expense.
One solution is to employ accelerometers which are not electrical or semiconductors in nature. The use of fiber optics for sensors in general, and for accelerometers in particular, are one option available to designers which simultaneously solves the EMI sensitivity, size and weight problems inherent in electrical sensors.
Since fiber optics use light rather than electricity, a fiber optic accelerometer is generally insensitive to EMI or EMF and are therefore more efficient in environments which have large amounts of electro magnetic energy. Therefore fiber optic accelerometers can be located adjacent to or actually attached to electronic devices which generate large electro magnetic fields without negative affects to either the accelerometer or the body of interest.
In “Design and Characterization of Fiber-Optic Accelerometers”. SPIE Volume 838, Fiber Optic and Laser Sensor V (1987), Miers, Ral, and Berthold disclose a microbend accelerometer having a fiber loop clamped between the two sets of corrugations. The Miers device also includes a second reference loop in the sensor element for the purpose of offsetting any spurious signals that are developed in the fiber-optic cable.
Therefore it is an object of this invention to offer an accelerometer device that is small and light weight.
It is yet a further object to offer an accelerometer that is EMI insensitive.
It is a further object of this invention to offer an accelerometer that features high levels of sensitivity.
It is a yet another object offer an accelerometer that is physical robust.
It is a further object of this invention to offer an accelerometer that is economical.